best way to collimate dobsonian

[Chippy3476 (Danial)]

Hi all,
I have just collimated my 114 newtonian using a home made colimating cap. It was hard at first but once I figured out what screw did what it got a little easier but was still reasonably frustrating.
I have a 8" dob that is still perfectly colimated according to my colimating cap but I was just wandering if anybody had some helpful hints and tips for colimating, any tools that would make it easier than just a cap? I have heard alot of bad things about lasers so I will avoid them, whats your thought on using a collimation cap?
The only thing that I find with the cap is it is very hard to see the 3mm eyehole reflection in the centre of the primary donut.
Thanks all
Dan

[rrussell1962]

On my Obsession I use a Farpoint laser to do a quick collimation and fine tune with a Cheshire tube. Laser is easy but the Cheshire tube gives a better result. Just my opinion. I have a spare Cheshire tube if you want to PM me.

[mental4astro (Alexander)]

Russell mentions Cheshire eyepieces - pretty much same thing as your homemade collimation cap, but on steroids. You can achieve all your collimation needs with it, but is a pain in the neck when you are way down at the primary mirror end of the scope, and you need to give your attention to the top. This is where a laser device is a good tool to have. Yes there are some problematic laser devices out there, but the short comings are easy to overcome. You might like to have a look at this following thread I started on tricking up a humble GSO laser collimation tool:

http://www.iceinspace.com.au/forum/s...ser+collimator

While this GSO collimation tool has short comings, it is a good and inexpensive way to start laser collimation. Just need a little TLC with it and it will be humming.

The main advantage of a cheshire, and you colli' cap too, is it will deal with the collimation of the secondary to the focuser where a laser won't.

Like Russell, I too use a laser and a cheshire eyepiece for my Newtonians

[Allan_L (Allan)]

A Simple Guide to Collimating a Newtonian Reflector

http://www.astro-baby.com/collimatio...on%20guide.htm

[mental4astro (Alexander)]

Allan, that is a great collimation how-to link,

Dan, note that the article in the link says that when you go through the collimation process, look at the situation of the secondary FIRST. Us Newtonian owners are often very guilty of neglecting the secondary's total situation, espeically if we use a laser, only tweaking the secondary's collimation bolts to get the laser centered on the primary. The laser will not collimate the secondary.

This took me a long time to understand, having used only a laser for a long time, yet the image I was seeing I could tell was still not perfect. I did first have a Cheshire eyepiece before the laser. Not completely understanding the collimation process, I ditched the Cheshire, and paid the consequences. I've now got two Cheshires, one 2" and a 1.25" for focusers of each type.

It does take a bit to get you head around at first as to what is going on with collimation, but once the penny drops you will slap your forehead and think - 'and that took me that long to figure out???!!!' Now the process for me takes moments, and is actually a welcome task at the start of the night's viewing as it gets me in tune with the scope and what is going on with it. Newtonians have several moving parts, and they do move.

Oh, and that homemade collimation cap of yours, you can paint a little white ring around the hole on the inside of the cap to help you see it better. Even better is to make a little ring from reflective tape (even if just square with a round hole punched out of it) and placed on the inside of the cap around the hole. If you like, I've got some reflective tape here at home, and I can make one for you and chuck it in the post. Let me know. I've done this to my 2" Cheshire and helps a lot.

One last thing, if you do end up getting a you-beaut Cheshire, don't ditch your homemade one. It may stay in the cupboard for a long time, but the time will come when you will need it... I've still got mine I made from an old Kodak film canister which still works fine.

Mental.

[MichaelSW (Michael)]

Dan,

Alex is Spot On with his advice to paint a white ring on the inside of your collimation cap around the hole as an aide to increase visibility. For my 35mm film canister, I painted the whole inside surface of the end white. Big improvement.

[rrussell1962]

I bought a cheap led torch from the supermarket with a lens about the same size as the hole on the cheshire tube and duct taped it on the hole, makes the visibility so much better. Eventually did away with the tape and just now hold it there.

[RobK (Rob)]

Thanks Alan for the link to
http://www.astro-baby.com/collimatio...on%20guide.htm

It was great help to get my head around the process

I did as was suggested took my time, collimating a 250mm dob, and think I have it fairly close.

Just waiting for the dust to clear to try it out

Rob

[ngcles]

Hi Danial & All,

Lots of good guides to collimation in links supplied above that should be enough to get you started. Best "manual" tool is a Cheshire eyepiece, not overly expensive, no batteries (to go flat at the worst possible moment) required. Lasers are just as good at achieving collimation, somewhat easier and more intuitive in use but equally somewhat more expensive (for a proper one that will hold its own collimation).

Tuning a telescope isn't hard and gets quicker with practise. It's a skill. Will probably take some time the first few attempts but eventually, you'll nearly be doing it with your eyes closed in a few moments.

As a side-note, I wish I had a dollar for every time a person has made the following comment, after I said something like "I think your telescope may be out of collimation":

"I was told they were colluminated at the factory"!


Best,

L.